1. Field of the Invention
The present invention relates to an apparatus for sensing incomplete molding of an automold system, and more particularly to an apparatus for sensing incomplete molding of an automold system, the apparatus including devices having a sensor and detect pin for detecting incompletely filled and fine unfilled junk portions of semiconductor packages. Each device is installed in an unloader unit of an automold system so as to efficiently sense fine incomplete filling of every package.
2. Description of the Prior Art
In a usual process for manufacturing semiconductor package, after a wire bonding procedure for electrically connecting semiconductor chips to inner leads of lead frames by means of a gold wire, a molding procedure for encapsulating the wire bonded chip and inner leads by using resin such as epoxy resin to protect them against outer circumstances (humidity, temperature. etc.) is carried out.
Such molding procedure is generally carried out by using an automold system. The automold system comprises a master mold die to be separated into a top mold die and a bottom mold die and an unloader unit which is adapted to take out packages of the bottom mold die after the molding procedure is completed in the master mold die.
Since the automold system does not have a separate apparatus for sensing incomplete molding of packages, incomplete molding of packages is sensed by determining whether every package is incompletely filled with compound when the package is taken out of cavity of the bottom mold die by the unloader unit.
Referring to FIG. 1, there is shown a conventional unloader unit of an automold system. As shown in the drawing, lower chassis 3 and 3' are formed with a plurality of cavities 3a each containing a molded package 2 and mounted on a bottom mold die 1. Above the bottom mold die 1 is located an unloader unit 6 which is moved leftward and rightward along a transfer guide 5 by driving a servomotor shaft 4.
The unloader unit 6 is provided with a vacuum system. The vacuum system comprises a micro ejector 7 attached to a front side of a vertical wall 6a of the unloader unit 6 which is adapted to control vacuum conditions and sense incomplete molding of packages, vacuum heads 9 and 9' mounted on a horizontal plate 6b of the unloader unit 6 and connected to the micro ejector 7 via a vacuum hose 8, and a plurality of vacuum pad guides 11 which protrude downward from the vacuum heads 9 and 9' and have at ends thereof vacuum pads 10 for generating vacuum suction force by control of the micro ejector 7 in order to suck and hold packages 2 received in the cavities 3a of the lower chassis 3 and 3'.
Also, the unloader unit 6 is provided with a micro switch (not shown) which is turned on/turned off to generate control signal depending upon whether suction force is normally generated in the micro ejector 7. Positioning bars 12 are fixed to the bottom mold die 1 in order to set precise position of the unloader unit 6 relative the bottom mold die 1. The micro ejector 7 is connected to an air hose 13 through which air is sucked and discharged via the vacuum pads 10 to hold and release the packages 2.
In the above-mentioned conventional apparatus for sensing incomplete molding, after molded packages 2 are sucked at the vacuum pads 10 and then sensed whether the packages 2 are completely filled with compound or not, the packages 2 are transferred to a gate brake unit (not shown) via a carrier unit (not shown).
An operation of the above known apparatus for sensing incomplete molding will be described with reference to FIGS. 1 and 2 as follows.
After molding procedure has been completed, a press is opened and a top mold die (not shown) is separated from the bottom mold die 1. Then, lead frames 14 are ejected from the chassis 3 and 3' of the bottom mold die 1 by means of eject pins. Since the lead frames 14 each are integrally formed with the package 2 molded in the cavity 3a, the packages 2 are also ejected from the cavities 3a by the ejection of the lead frames 14.
Thereafter, the unloader unit 6 is moved to and located above the bottom mold die 1. Then, the bottom mold die 1 is raised such that the positioning bars 12 fixed to the bottom mold die 1 are inserted into holes formed at the horizontal plate 6b of the unloader unit 6, thereby causing upper surfaces of the packages 2 to be closely contacted with the vacuum pads 10.
Subsequently, the micro ejector 7 of the vacuum system is operated to produce a vacuum in the vacuum heads 9 and 9'. As a result, the vacuum pads 10 generate suction force so that the packages 2 is sucked or held at the vacuum pads 10.
At this time, normally molded package 2 is forcibly sucked and held at the vacuum pad 10 because normal suction force is generated in the micro ejector 7. As a result, since the normal suction force is sensed by a micro switch (not shown), it is indicated that the package has been normally molded. In this case, the indication of normality/abnormality of molding is displayed from a CRT or a display unit by control of a controller (not shown) in response to output signal of the micro switch.
On the other hand, as shown in FIG. 2, when a package has been incompletely molded so that the package has an incomplete filling portion (hatching portion in the drawing), the package is not sucked and held at the vacuum pad 10 because abnormal suction force is generated in the vacuum pad 10 due to the unfilled portion of the package. Accordingly, the abnormal suction force is also generated in the micro ejector 7. As a result, the micro switch (not shown) senses the abnormal suction force and then generates an error signal indicating that the package has been incompletely molded, thereby indicating presence of the unfilled portion in package.
However, although the above conventional apparatus for sensing incomplete molding can sense an abnormal package when the package has a large unfilled portion as shown in FIG. 2, the apparatus can not sense an abnormal package when the package has a fine unfilled portion so that a number of poor packages may be produced.
Also, since the apparatus has not the number of vacuum pads corresponding to the number of packages but a predetermined number of vacuum pads per a lead frame, the apparatus can not sense every poor package.
In addition, when the vacuum pad guides 11 connected to the vacuum heads 9 and 9' are blocked due to foreign substance which damage the vacuum pads, the apparatus can not sense poor package.